Numerous different apparatus for washing garments and fabrics are known. Examples of patents on washing machines include U.S. Pat, No. 1,358,168 to McCutchen, U.S. Pat. No. 1,455,378 to Allen, U.S. Pat. No. 2,357,909 to Ridge, U.S. Pat. No. 2,816,429 to Kurlancheek, and U.S. Pat. No. 3,444,710 to Gaugler. Such apparatus is, in general, adapted to home use with water-based cleaning systems.
Non-aqueous cleaning apparatus, known as "dry cleaning" apparatus, is also known. Dry cleaning employs an organic solvent such as perchloroethylene in place of an aqueous system. Dry cleaning apparatus is not, in general, employed in the home, and is instead situated at a store or central plant. Problems with convention dry-cleaning systems include the toxic nature of the solvents employed.
Carbon dioxide has been suggested as a dry cleaning medium. See, e.g., U.S. Pat. No. 4,012,194 to Maffei. One apparatus is described in U.S. Pat. No. 5,467,492 to Chao et al. This apparatus has apparently been supplanted by the apparatus described in U.S. Pat. No. 5,669,251 to Townsend et al. Townsend describes a dry cleaning system having a hydraulically rotated basket that rests on roller bearings. U.S. Pat. No. 5,267,455 to Dewees et al. describes a dry cleaning system in which carbon dioxide as a cleaning medium is transferred between vessels by means of a second purge gas such as nitrogen. U.S. Pat. No. 5,850,747 to Roberts et al. describes a carbon dioxide cleaning system incorporating a temperature compensating compressor. PCT Application WO 97/33031 to Taricco describes a super-cooled fluid temperature controlled cleaning system. None of these references provides a substantial discussion of how to control a carbon dioxide cleaning apparatus.
PCT Application WO 99/13148 to S. Shore describes a dry cleaning system that cycles through eight modes, including a loading (or "idle") mode, a prefill mode, a pressurization mode, a wash mode, a reclaim mode, a vent mode, a make-up mode (or storage fill mode) and a distillation mode. It will be noted from FIG. 3A and FIG. 8 therein that, during the idle mode, numerous valves (including valves 9, 11, 18, 20, 22, 27, 29, 35 and 49) are maintained in a closed position. This creates enclosed areas within the pipes and ancillary vessels of the apparatus. While acceptable for short term periods, it will be readily seen that it is undesireable to create enclosed spaces that are potentially charged with a pressurized gas in such a large industrial apparatus during prolonged periods of idleness (e.g., during night time, holidays, power failures, etc.). The risks of creating such enclosed pressurized chambers are exacerbated if apparatus is then held in an elevated temperature environment, as may well be found in a cleaning plant.
Accordingly, there is a need for improved carbon dioxide cleaning systems that are equipped for periods of sustained idleness or inactivity, whether expected or unexpected, and methods of operating such equipment.